Gas-cooled nuclear reactors employ a coolant, such as helium or carbon dioxide, to remove the heat of fission from a nuclear reactor core and transfer it via heat-exchangers located within a concrete pressure vessel to a secondary fluid coolant, with a primary circulation system being used to achieve a desired continuous gas flow pattern within the concrete pressure vessel. If during an emergency the primary circulation systems fails to continue to operate, the reactor will be automatically shut down; the reactor core will continue to produce decay heat. The decay heat must be removed from the core during shutdown, and various systems have been proposed for this purpose. U.S. Pat. No. 4,299,660 issued Nov. 10, 1981 to Quade illustrates an emergency system wherein additional coolant circulators are actuated to circulate gas coolant into the concrete pressure vessel, through the core and out of the concrete pressure vessel to an auxiliary heat dump. Improved emergency shutdown systems for relatively small size reactors, i.e., about 100 to 400 MWt (megawatts) are desired.